The study examines the potential interactions between the zwitterions ciprofloxacin, levofloxacin and trovafloxacin and the cation procainamide in proximal renal tubule. Eight young (18-40 years) and 8 elderly (+65 years) subjects will be enrolled. Pharmacokinetic parameters for procainamide and n-acetylprocainamide (NAPA) alone and in combination with each fluoroquinolone will be calculated. Mean pharmacokinetic parameters for procainamide will be compared to combination parameters. Comparisons of mean pharmacokinetic values for the elderly and young groups will be made. This is significant because of the narrow therapeutic index of procainamide (and NAPA) and the increased risk of toxicity associated with elevated serum levels of procainamide.